Electroluminescent materials based on bis-(2-oxybenzyliden-4-tert-butyl aniline) zinc and on a luminescent additive, such as “Nile Red” dye, present in an amount in the range about 0.1 wt. % to about 5 wt. % are disclosed in Russian Patent No. RU 2,155,204. These materials emit in the red spectrum area (about 632 nm). There are several disadvantages associated with these materials, such as a lack of mechanical strength. This occurs because the material is a mixture of two low molecular weight substances.
Additionally, luminescent materials capable of electroluminescence consisting of an organic semi-conductive component and a luminophore are disclosed in Japan Patent No. JP 9082473 and European Patent Application publication No. EP 0669387. The disadvantages of these materials include that the main emission bands are caused by the luminophore and there are undesirable bands caused by the semi-conductive component in the luminescence spectra.
Furthermore, luminescent organo-siloxane polymer materials and methods for fabricating the materials are disclosed in U.S. Pat. No. 6,361,885. Here, the main chain of the polymer contains a covalently bounded organic component which is capable of luminescence and which consists of two or more condensed aromatic rings containing substituents. The light emitting polymer may be produced by re-distillation of 9,10-bis(3-trichlorosilylpropyl)anthracene synthesized by a multi-step method on a glass substrate at a high temperature and at a residual pressure of about 10−6 Torr. Then, the re-distilled layer is maintained in air for 15 minutes and then is heat-treated at about 110° C. for about 30 minutes. The resultant polymer possesses a weak pale-violet luminescent emission in a spectrum region of about 370 nm to about 430 nm. The complex multi-step production method of the starting monomer and the polymer as well as low emission intensity are major disadvantages of these polymer materials.
Also known are luminescent polymer materials containing repeated arylene-vinylene fragments and fluorinated tetraphenyl fragments. These materials are generated by the copolymerization of the fluorinated tetraphenyl derivative with a dialdehyde containing two arylene groups as disclosed in U.S. Pat. No. 6,495,273. Here, the fluorinated tetraphenylene derivative is obtained from 1,22-bis(bromomethyl)-8,9,11,1-2,14,15,17,18-octafluorotetraphenyl in the presence of triphenyl phosphine. The light emitting polymer material is obtained by reaction of the monomer with arylenealdehyde where the arylene groups may include thiophene, phenyl, and carbazole, for example. Thin films for electoluminesence are produced from a solution using the spin-coating technique. The emission spectrum region of the material is about 250 nm to about 490 nm. The disadvantages associated with these materials are that the starting compounds are not easily available and additional steps are required to remove traces of solvent and catalyst.
Light emitting materials based on derivatives of diketopyrrolo-(3,4-c)-pyrrole containing a pyrromethene complex are disclosed in U.S. Patent Application Publication No. 2003/0082406 A1. In this case, the dilketoptyrrolo-(3,4-c)-pyrrole derivatives used include different alkyl substituents having a number of carbon atoms in the range of about 1 to about 25, and where the derivatives are not polymers. The pyrromethene complex is added to the diketopyrrolo-(3,4-c)-pyrrole derivative in an amount of about 0.1 wt. % to about 1 wt. %. The luminescence of the resultant material is in a yellow-red region (about 580 nm to about 720 nm). A disadvantage of these luminescent materials is that the diketopyrrolo-(3,4-c)-pyrrole derivatives are not easily available. Additionally, due to low molecular weight, the organic material does not provide good mechanical strength in the form of a luminescent layer.
A method of preparing a material based on 3-hydroxyflavone, where the emission region is about 375 nm to about 475 nm, by high frequency magnetron sputtering from the surface of aluminum target in the flow of a gas-carrier which is a mixture of about 95% Ar and about 5% O2 is known. This method is performed in the following manner. A high-power high-frequency discharge (about 13.56 MHz or about 600 W) in a reaction chamber is evacuated to about 10−5 Pa by placing the 3-hydroxyflavone powder on the target for magnetron sputtering. The power used during sputtering of the dye is not less than about 10 W to about 30 W. The use of such large power, however, causes partial destruction of 3-hydroxyflavone as can be seen from the gas phase mass-spectrums. The disadvantages of this method are that the resultant luminescent material is unstable during storage and a deterioration of the emission characteristics occurs after maintaining the material in air for several hours. Additionally, the light emitting material changes appearance from an initially smooth and uniform film to a spongy and powder-like film. Also, further disadvantages include a large energy consumption and high working frequency (about 13.56 MHz) which, when used in a commercial scale equipment, requires the use of special safety means for protection of the personnel. The other drawback is that the method requires the use of a special gas-carrier (argon).